Athletic Club, commonly known as just Athletic domestically and often as Athletic Bilbao abroad, is a professional football club based in the city of Bilbao in the Basque Country, Spain. They are known as Los Leones because their stadium was built near a church called San Mamés, which was named after Saint Mammes, an early Christian thrown to the lions by the Romans. Mammes pacified the lions and was later made a saint. The team plays its home matches at the San Mamés Stadium. Its home colours are red and white-striped shirts with black shorts.

Bilbao is a city in northern Spain, the largest city in the province of Biscay and in the Basque Country as a whole. It is also the largest city proper in northern Spain. Bilbao is the tenth largest city in Spain, with a population of more than 347,000 as of 2023. The Bilbao metropolitan area has 1,037,847 inhabitants, making it the most populous metropolitan area in northern Spain; with a population of 875,552, the comarca of Greater Bilbao is the fifth-largest urban area in Spain. Bilbao is also the main urban area in what is defined as the Greater Basque region.